Fibrous nonwoven materials and fibrous nonwoven composite materials are widely used in disposable wipers. Several methods are used for producing these fibrous nonwoven materials. In one approach, called air laid, wood fibers are bonded together into a web using an adhesive emulsion. This web must be dried to remove the water and set the adhesive. The resulting web tends to be stiff, due to the presence of the adhesive that binds all of the fibers.
Another approach, called spunlacing, employs jets of high velocity water to mechanically interlock the fibers in the web. This process commonly uses staple fibers and wood fibers as components in the web. Continuous filaments produced by the spunbond process can also be combined with wood fibers in the spunlacing process. Because adhesive is not commonly used in the spunlacing process, the fibers have substantial freedom to bend and twist, and the resulting webs are soft and drapeable. However, synthetic fibers are significantly more expensive than wood fibers and the spunlacing process has high capital and operating costs.
A third approach used to prepare absorbent nonwovens is to form a blend of absorbent fibers and synthetic fibers produced by the meltblowing process. This type of pulp-polymer integrated composite, called coform, consists of an air formed matrix comprising meltblown microfibers having an average diameter of less than 10 microns, and a multiplicity of individualized absorbent fibers such as, for example, wood pulp fibers, disposed throughout the matrix of polymer microfibers and engaging at least some of the microfibers to space the microfibers apart from each other. The absorbent fibers are interconnected by and held captive within the matrix of microfibers by mechanical entanglement of the microfibers with the absorbent fibers, the mechanical entanglement and interconnection of the microfibers and absorbent fibers alone forming a coherent integrated fibrous structure. These materials are prepared according to the descriptions in U.S. Pat. No. 4,100,324 to Anderson et al. Patents describing the use of coform nonwoven materials and composite fabrics incorporating coform layers include U.S. Pat. Nos. 4,663,220; 4,784,892; 4,906,513; 5,952,251; 6,028,018; 6,946,413 and U.S. Patent Publication Application No. US 2005/0266760A1. Coform nonwovens have good absorbency properties and have been successfully used in the manufacture of absorbent wipes.
Coform has the advantage of combining relatively low cost raw materials with a process that is relatively low in capital cost. Because the meltblown fibers are thermoplastic, they can be used to strengthen the air formed matrix by thermal bonding. Heat embossing coform webs is commonly practiced.
A disadvantage of coform is that the composite tends to be stiff, and this stiffness is aggravated by heat embossing. One prior approach to addressing this disadvantage entails producing a composite incorporating a stretched elastic component bonded to one or more coform layers, as described for example in U.S. Pat. No. 6,946,413. After the bonding is complete, the tension on the elastic component is released, producing a soft, bulky stretch-bonded laminated fabric. Disadvantages of the stretch-bonded laminate approach include the high capital cost of the process and the high cost of the elastomer component.